Andreas Schneemann

Zinc-1,4-benzenedicarboxylate-bipyridine frameworks – linker functionalization impacts network topology during solvothermal synthesis

Substitution of 1,4-benzenedicarboxylate (bdc) with additional alkoxy chains is the key to construct a family of metal–organic frameworks (MOFs) of the type [Zn2(fu-bdc)2(bipy)]n (fu-bdc = functionalized bdc; bipy = 4,4′-bipyridine) exhibiting a honeycomb-like topology instead of the default pillared square-grid topology. Both the substitution pattern of the phenyl ring of the fu-bdc linker and the chain length of the alkoxy substituents have a major impact on the structure of the derived frameworks. Substitution at positions 2 and 3 leads to the trivial pillared square-grid framework, and substitution at positions 2 and 5 or 2 and 6 yields MOFs with the honeycomb-like topology. Also, simple methoxy substituents lead to the construction of a pillared square-grid topology, whereas longer substituents like ethoxy, n-propoxy, and n-butoxy generate honeycomb-like framework structures. These honeycomb MOFs feature one-dimensional channels, which are tuneable in diameter and functionality by the choice of substituent attached to the bdc-type linker. Pure component sorption isotherms indicate that the honeycomb-like frameworks selectively adsorb CO2 over N2 and CH4.

Targeted Manipulation of Metal–Organic Frameworks To Direct Sorption Properties

Metal-organic frameworks are promising materials for manifold applications. This Minireview highlights approaches for the fine-tuning of specific sorption properties (e.g. capacity, selectivity, and breathing behavior) of this interesting class of materials. Central aspects covered are the control over the crystal morphology, the targeted tuning of sorption properties by judicious choice of metal centers and linkers, and the preparation of host-guest systems. We want to introduce the reader to these topics on the basis of the manipulation of a handful of outstanding prototypical metal-organic frameworks.

Influence of Solvent-Like Sidechains on the Adsorption of Light Hydrocarbons in Metal–Organic Frameworks

A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal-organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low-density solvent with restricted degrees of freedom, offer tunable control of dispersive host-guest interactions. The performance of a series of frameworks of the type Zn2 (fu-bdc)2 (dabco) (fu-bdc(2-) =functionalized 1,4-benzenedicarboxylate; dabco=1,4-diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold.

Influence of Co-adsorbates on CO2 induced phase transition in functionalized pillared-layered metal–organic frameworks

Most studies on flexible MOFs which suggest good separation properties of the framework are solely based on single component isotherms and conclusions drawn from these. However, many factors are not considered, particularly the change of the pore space after the opening of the framework can have a distinct effect on the adsorption of a second gas present in a real separation problem that does not induce the phase transition of the material. Within this study, we focus on a series of flexible pillared-layered MOFs of the type [Zn2(fu-bdc)2(dabco)]n bearing flexible side chains and analyze the gas adsorption behavior when the material is exposed to mixtures of CO2 with other adsorptives, including N2, CH4, C2H6 and C3H8, to evaluate the influence of the co-adsorbate on the sorption selectivity and phase transition under these conditions.